(a) Field of the Invention
The present invention relates to a dry sewing machine, or a sewing machine which can be operated without oiling. The machine of the preferred embodiment is particularly adapted for making a type 401 two thread chain stitch, used in commercial sewing operations. In addition to employing sealed bearings, novel spreader and rocker frame assemblies are employed.
(b) Description of the Prior Art
The present invention relates to a dry sewing machine. Known commercial sewing machines, such as the model 300U made by The Singer Company, often have 15 or more oiling points, which should be oiled every 8 or so hours of operation, causing machine downtime. Some machines, such as the 300W made by The Singer Company, employ oil pans and wicking systems to transfer oil to parts needing oil. Because commercial sewing machines are sometimes employed with other machines, such as a tape edge machine used in sewing mattress covers, where the machine is not "level" during operation, the effectiveness of an oil pan and wicking system can be reduced, leading to wear on the parts needing to be oiled.
In making a 401 chain stitch, an upper thread and a lower thread are used. The upper thread passes through the needle eye and the lower thread passes through the looper eye. A spreader is employed to position the lower thread on the correct side of the needle during the sewing operation. Typically, in commercial sewing, about six or seven 401 chain stitches per inch are made. Various sewing manuals describe the 401 chain stitch and how it is made. For example, the Union Special Corporation has a 1976 copyrighted booklet entitled Stitch Formation, Type 401, incorporated herein by reference.
The needle, spreader, and looper operate in concert to make the stitch, all making one coordinated cycle. In one coordinated cycle, when looking at the front of the sewing machine, the needle moves from high position to low position to high position, the looper moves from almost far left position to far left position to far right position to almost far left position, and the looper moves from far forward position to furthest back position to far forward position. For example, the spreader moves a total distance of about 1/4 inch or 6.35 mm from its far left position, which is to the left of the needle and left of the looper, to its far right position, to the right of the needle. The looper is to the left of the needle. A compound material feeding system exists, as the needle, presser foot, and lower feed dog operate in unison.
In commercial sewing machine models made by The Singer Company, such as the model 300U103, a comparatively complicated eccentric mechanism is employed to accomplish the spreader left/right movement. This mechanism requires oiling. Simply, an off-centered wheel on a main shaft causes a first transverse shaft to oscillate back and forth. The first shaft is connected to a transverse second shaft which holds the spreader. This second shaft, and therefore the spreader, moves back and forth the entire required 1/4 inch or 6.35 mm.